ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
ilogb(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_ISOC99_SOURCE; or cc -std=c99
ilogbf(), ilogbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
|| _ISOC99_SOURCE; or cc -std=c99
These functions return the exponent part of their argument as a signed
integer. When no error occurs, these functions are equivalent to the
corresponding logb(3) functions, cast to int.
On success, these functions return the exponent of x, as a signed
If x is zero, then a domain error occurs, and the functions return
If x is a NaN, then a domain error occurs, and the functions return
If x is negative infinity or positive infinity, then a domain error
occurs, and the functions return INT_MAX.
See math_error(7) for information on how to determine whether an error
has occurred when calling these functions.
The following errors can occur:
Domain error: x is 0 or a NaN
An invalid floating-point exception (FE_INVALID) is raised.
These functions do not set errno for this case.
Domain error: x is an infinity
These functions do not set errno or raise an exception for this
log(3), logb(3), significand(3)
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